Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$243.54	5.157%	$256.0994	$256.10	$256.10	$256.10
Purchase #2	$36.64	6.210%	$38.9153	$38.92	$38.90	$38.90
Purchase #3	$129.93	9.522%	$142.3019	$142.30	$142.30	$142.30
Purchase #4	$73.44	12.731%	$82.7896	$82.79	$82.80	$82.80
Purchase #5	$232.30	10.498%	$256.6869	$256.69	$256.70	$256.70
Purchase #6	$225.94	6.305%	$240.1855	$240.19	$240.20	$240.20
Purchase #7	$223.67	7.127%	$239.611	$239.61	$239.60	$239.60
7 purchase totals =	$1,165.46		$1,256.5896	$1,256.60	$1,256.60	$1,256.60